Sheet feeder and image forming apparatus having the same

ABSTRACT

A device for supplying sheets including a main body; a sheet feed cassette; a lift plate; a lift plate lifter mechanism; and a drive device for the mechanism; in which a lift side coupling gear is engaged with a drive side coupling gear of the drive device when the sheet feed cassette is stored in the main body, and is displaceably supported in a direction of toward and away from with respect to the drive side coupling gear in a range where the engagement of the gears is not released.

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2008-154410, filed Jun. 12, 2008, the entire contents of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a device for supplying sheets of paper or the like which can be used with an image forming apparatus such as a copying machine or a printer. The present invention also relates to an image forming apparatus having the device for supplying sheets.

2. Description of the Related Art

In image forming apparatus, such as copying machines or printers, a device for supplying sheets is essential for feeding sheets of paper. In many cases, the device, in the image forming apparatus, stocks a large number of unprinted sheets in a storage unit, and separates and supplies the stacked sheets from the topmost layer, sheet by sheet. Devices of this type are used in image forming apparatuses including cassette type feed units, manual feed units, and document feed units.

Methods of removing the sheets from the device for supplying sheets include roller supply systems and suction supply systems. The roller supply system is generally widely used. In the roller supply system, a pickup roller located upstream is brought into contact with the topmost layer of a bundle of sheets. The sheet is delivered to a sheet feed roller located downstream and the sheet is removed from the device for supplying sheets by means of the sheet feed roller.

Methods of bringing the topmost layer of the bundle of sheets in contact with the pickup roller include a method of urging a lift plate on which the sheets are stacked up from a lower portion thereof by a drive device provided with a motor or the like. Additionally, methods include pushing the lift plate up by means such as a spring. When the lift plate moves up to a sheet supply position in the sheet feed cassette, the drive device is mounted outside the sheet feed cassette and in the main body of the device for supplying sheets, or within the image forming apparatus that includes the device.

In the device for supplying sheets, typically, when the sheet feed cassette, that is stored in the image forming apparatus, is pulled out therefrom, the withdrawal operation might feel difficult and very heavy due to the design of the drive device for the lift plate. Therefore, in the prior art, a lifter for a sheet feed cassette intermediate plate detects when a user puts his hand on a knob in order to pull out the sheet feed cassette. The lifter then rotates the lift motor in a direction so that the intermediate plate (lift plate) comes down. At the same time, the lifter releases the coupling of gears that drive the intermediate plate. The sheet feed cassette can then be smoothly pulled out. However, in the above-mentioned configuration, in order to release the coupling of the lift plate and the drive device, an arrangement of the sensor with respect to a portion of the knob, and a complicated design of the gears of the drive device to allow the release are required. As a result, the cost of the part, as well as production costs can substantially increase.

It is also known in the prior art, in devices for feeding sheets to provide an intermediate gear which is a part of a drive mechanism for transmitting power to the lifter that raise and lowers the intermediate plate (lift plate). With the above-mentioned design, the intermediate plate can be raised and lowered by the drive mechanism when the sheet feed cassette is stored in the apparatus main body. The intermediate plate is lowered due to gravitational force when the sheet feed cassette is pulled out. Accordingly, when the sheet feed cassette is pulled out, the withdrawal operation does not feel heavy, and the sheet feed cassette can be relatively smoothly pulled out. However, when the sheet feed cassette is stored in the apparatus main body, there is a substantial possibility that the teeth of the intermediate gear located in the sheet feed cassette can collide with the teeth of the gears on the apparatus main body side which engage with the teeth of the intermediate gear. Therefore, it is possible that the paper feed cassette cannot be stored at a given position. Further, the gears for driving the lift plate can be damaged due to repeated storage operations causing the sheet feeding operation not to function properly.

SUMMARY

The present invention provides a device for supplying sheets having a drive device which pushes a lift plate up and displaces the lift plate to a sheet supply position. The device is capable of a smooth withdrawal and storage of a sheet feed cassette, as well as capable of readily storing the sheet feed cassette at an appropriate position. Moreover, the device can perform stable sheet feeding operations. These features can be provided with a simple design and reduction in cost. In an embodiment, the present invention provides an image forming apparatus provided with the device for supplying sheets.

According to an embodiment, the present invention provides a device for supplying sheets includes: a sheet feed cassette in which sheets are stacked, and which can be pulled out and stored in a direction parallel to a sheet conveying direction with respect to the main body of an apparatus; a lift plate located within the sheet feed cassette and having a top surface on which the sheets are placed; a lift plate lifter mechanism which is located in the sheet feed cassette, for moving up the lift plate to displace the lift plate to a sheet supply position; and a drive device which is located in the main body of the apparatus, for providing power to the lift plate lifter mechanism. The drive device includes a drive side coupling gear that is coupled with the lift plate lifter mechanism when the sheet feed cassette is stored in the apparatus main body. The lift plate lifter mechanism comprises a lift side coupling gear which is located at a side surface of the sheet feed cassette, engaged with the drive side coupling gear of the drive device when the sheet feed cassette is stored in the main body, and is displaceably supported in a direction toward and away from with respect to the drive side coupling gear in a range where the engagement is not released. Accordingly, a slight gap is defined between the drive side coupling gear and the lift side coupling gear engaged each other. As a result, there is a gap with respect to the rotation between both of these gears, thereby making it possible to prevent a high load from being applied when the sheet feed cassette is withdrawn from the apparatus and preventing the teeth of both the gears from colliding with each other when the sheet feed cassette is stored in the apparatus main body. The support mechanism of the lift side coupling gear can be obtained with a simple design. Accordingly, with a simple design that reduces the cost, the withdrawal and storage of the sheet feed cassette can be easily accomplished, the sheet feed cassette can be readily stored at an appropriate position, and the device for supplying sheets is capable of performing a stable sheet feeding operation.

The sheet feed cassette has an elongated hole on the support portion of the lift side coupling gear. The elongated hole allows a displacement the lift side coupling gear in a direction further toward and away from with respect to the drive side coupling gear. As a result, with a simpler design, a support mechanism of the lift side coupling gear can be provided. Therefore, with a design that further reduces the costs, the withdrawal and storage of the sheet feed cassette can be smoothly performed, and the sheet feed cassette can be stored at an appropriate position with ease.

The elongated hole extends in a direction that the lift side coupling gear separates from the drive side coupling gear while rotating when the lift side coupling gear and the drive side coupling gear come in contact with each other. This design enhances the prevention of the teeth of the lift side coupling gear and the drive side coupling gear from colliding with each other when the sheet feed cassette is stored in the main body of the apparatus. It should be noted that the lift side coupling gear and the drive side coupling gear are easily engaged with each other. Accordingly, the storage of the sheet feed cassette can further be smoothly performed, thereby enabling the advantageous effect of storing the sheet feed cassette at an appropriate position, and improving a stable sheet feed operation.

When the lift side coupling gear rotates due to the drive device, the coupling gear is displaced in a direction toward the drive side coupling gear due to rotation force. As a result, even though a gap is provided between the lift side coupling gear and the drive side coupling gear which are engaged with each other, both gears are easily engaged. Accordingly, there can be provided a device for supplying sheets that is capable of performing a stable sheet feeding operation.

Since the device for supplying sheets is mounted on the image forming apparatus, with a simple design that reduces cost, the withdrawal and storage of the sheet feed cassette can be smoothly performed, and the sheet feed cassette can be easily stored at an appropriate position, whereby the image forming apparatus is capable of performing a stable sheet feeding operation.

Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

In the accompanying drawings:

FIG. 1 is a schematic vertical right side view illustrating a printer to which a device for supplying sheets according to an embodiment of the present invention is mounted;

FIG. 2 is a rear perspective view illustrating a right side of the device for supplying sheets illustrated in FIG. 1;

FIG. 3 is a rear perspective view illustrating a right side of the sheet feed cassette illustrated in FIG. 2;

FIG. 4 is a front perspective view illustrating a lift plate lifter mechanism of the sheet feed cassette illustrated in FIG. 3;

FIG. 5 is a front perspective view illustrating the periphery of the lift plate lifter mechanism of the sheet feed cassette portion illustrated in FIG. 3;

FIG. 6 is a perspective view illustrating a drive device of the lift plate lifter mechanism viewed from the inside (sheet feed cassette side);

FIG. 7 is a perspective view illustrating a statement of engagement of the lift plate lifter mechanism and the drive device thereof viewed from the inside (sheet feed cassette side);

FIG. 8 is a perspective view illustrating the periphery of the lift plate lifter mechanism of the sheet feed cassette front portion which is the same as that in FIG. 5;

FIG. 9 is a partially enlarged view illustrating portions of a lift side coupling gear and a drive side coupling gear viewed from the inside;

FIG. 10 is a partially enlarged view illustrating the portions of the lift side coupling gear and the drive side coupling gear which are the same as those in FIG. 9 viewed from the inside in a state where both gears are separated from each other; and

FIG. 11 is a partially enlarged view illustrating the portions of the lift side coupling gear and the drive side coupling gear which are the same as those in FIG. 9 viewed from the inside in a state where both gears are rotating.

DETAILED DESCRIPTION

Hereinafter, a description is provided of an embodiment of the present invention with reference to FIGS. 1 to 11. In the present invention, it is assumed that a device for supplying sheets, according to an embodiment of the present invention, is located on a bottom of an image forming apparatus (printer).

First, with reference to FIG. 1, a description is provided of image output operation in a printer, which is an example of an image forming apparatus, in which the device for supplying sheets according to the present invention is mounted. FIG. 1 is a schematic vertical right side view illustrating a printer in which a device for supplying sheets according to an embodiment of the present invention is mounted. In FIG. 1, the left side is a front side of the printer whereas the right side is a rear side thereof.

As illustrated in FIG. 1, a device for supplying sheets 20 is located on a bottom of a printer 1. In the device for supplying sheets 20, a sheet feed cassette 22 is located inside a main body 21 of the device for supplying sheets 20. Sheets P, such as unprinted cut papers, are stacked and positioned within the sheet supply cassette 22. A sheet feed portion 23 is located downstream of the sheet feed cassette 22, in a sheet conveying direction, that is, on the left and upper side of the sheet feed cassette 22 in FIG. 1. The sheets P are fed out separately one by one toward the left and upper side of the sheet feed cassette 22 in FIG. 1. The sheet feed cassette 22 can be pulled out from and stored in the main body 21 by sliding horizontally toward a front side of the main body 21, that is, toward the left side in FIG. 1.

A manual sheet feed tray 2 is located on a front and center portion of the printer 1. The manual sheet feed tray 2 is designed to be rotatable about a spindle that is located on a lower end thereof and extends substantially horizontally in the sheet width direction. The manual sheet feed tray 2 has an upper end that is opened and closed about the spindle in the outward direction of the printer 1. The sheets P, or the like, can be put on the upper surface thereof by opening the manual sheet feed tray 2.

On the manual sheet feed tray 2, a sheet to be fed one at a time, for example, sheets having an atypical size not included in the specification of the sheet feed cassette 22, is placed. The sheet on the manual sheet feed tray 2 is fed out toward the right side in the figure by means of the sheet feeder 3 for the manual sheet feed tray 2 which is located on the right side of the manual sheet feed tray 2 in FIG. 1. The manual sheet feed tray 2 is closed as illustrated in FIG. 1 when not in use.

Downstream of the sheet feed cassette 22 and the manual sheet feed tray 2, are a sheet conveying path for sheet feed 4, a resist roller 5, an image formation unit 30, and a transfer roller 6. The sheet P that has been fed from the sheet feed cassette 22 and the manual sheet feed tray 2 is fed to the resist roller 5 through the sheet conveying path for sheet feed 4. The resist roller 5 feeds the sheet P to a transfer nip portion formed by being photosensitive drum 31 and the transfer roller 6, that serves as a transfer member, in contact against each other by pressure in synchronism with a toner image formed in the image formation unit 30 while correcting the diagonal feed of the sheet P.

An image data signal, for example a character, graphic, or pattern, is transmitted to the printer 1 from an external computer (not shown), and a laser beam L (indicated by a chain line in the figure) controlled by an optical unit 7, which is located on an upper portion of the image formation unit 30, is irradiated based on the image data. Using this design, in the image formation unit 30, an electrostatic latent image of an original image is formed on the photosensitive drum 31, which is an image carrier, and a toner image is developed from the electrostatic latent image. The toner image is transferred to the sheet P, fed by the resist roller 5, in synchronization at the transfer nip portion

Downstream of the image formation unit 30 and the transfer roller 6, in the sheet conveying direction, is located a fixing unit 8. The sheet P, conveying an unfixed toner image by means of the transfer nip portion, is fed to the fixing device 8. The toner image is then heated and pressurized by the heat roller and the pressure roller, and fixed to the sheet P.

Downstream of the fixing device 8 a discharge sheet conveying path 9, a sheet discharge portion 10, and a sheet discharge portion 11 are positioned. The sheet P, discharged from the fixing device 8, is fed upward through the discharge sheet conveying path 9, and then discharged to the sheet discharge portion 11 located on an upper surface of the printer 1.

The design of the device for supplying sheets 20 that is mounted in the printer 1 will now be described with reference to FIG. 1 as well as FIGS. 2 to 7. In the figures, FIG. 2 is a rear perspective view illustrating the right side of the device for supplying sheets viewed backward. FIG. 3 is a rear perspective view illustrating the right side of a sheet feed cassette. FIG. 4 is a front perspective view illustrating a lift plate lifter mechanism. FIG. 5 is a front perspective view illustrating the periphery of the lift plate lifter mechanism of the sheet feed cassette front portion. FIG. 6 is a perspective view illustrating a drive mechanism of the lift plate lifter mechanism viewed from the inside (sheet feed cassette side). FIG. 7 is a perspective view illustrating the engagement of the lift plate lifter mechanism and the drive device thereof view from the inside (sheet feed cassette side).

The device for supplying sheets 20 is located at a lower portion of the interior of the printer 1 illustrated in FIG. 1 as described above. As illustrated in FIG. 2, the device for supplying sheets 20 has a flat rectangular structure, and is equipped with the printer 1. The device for supplying sheets 20 includes a drive device 50 (see FIG. 6) of the lift plate lifter mechanism 40 (see FIGS. 4 and 5) described later in addition to the main body 21, the sheet feed cassette 22, and the sheet feed unit 23 described above.

As illustrated in FIG. 3, the sheet feed cassette 22 has a flat box structure having an open upper surface. The sheets P are stacked in the sheet feed cassette 22. The sheet P is fed toward the left side from the right side in FIG. 3 by means of the sheet feed unit 23 illustrated in FIG. 1. At the side surfaces of the sheet feed cassette 22, there are provided horizontal projection stripes 24 that allow the sheet feed cassette 22 to slidably move substantially horizontally with respect to the main body 21 of the device for supplying sheets 20. The horizontal projection stripes 24 extend in the sheet conveying direction of the sheet feed cassette 22, that is, the direction of the arrow in FIG. 3.

Guide rails (not shown) are located inside the main body 21 of the device for supplying sheets 20 illustrated in FIG. 2 and at portions facing the side surfaces of the sheet feed cassette 22. The guide rails extend in the sheet conveying direction, that is, substantially horizontally in the longitudinal direction of the sheet supplying device 20. The guide rails engage with the horizontal projection stripes 24 located on the side surfaces of the sheet feed cassette 22. This enables the withdrawal and storage of the sheet feed cassette 22 with respect to the main body 21 in a direction parallel to the sheet conveying direction. The horizontal projection stripes 24 and the guide rails are located on both the right and left side surfaces of the sheet feed cassette 22.

As illustrated in FIG. 3, a lift plate 25 is located inside the sheet feed cassette 22. The sheets P are placed on the lift plate 25. The lift plate 25 is supported by both side surfaces of the sheet feed cassette 22 at an upstream end thereof in the sheet conveying direction, and is rotatable about a spindle 25 a (see FIG. 1) along the sheet conveying direction with the free end being downstream.

A lift plate lifter mechanism 40 illustrated in FIGS. 4 and 5 is mounted at a lower portion of the downstream end of the lift plate 25 and at the downstream portion of the sheet feed cassette 22. The lift plate lifter mechanism 40 includes a push-up plate 41, a rotation shaft 42, a fan-shaped gear 43, and a lift side coupling gear 44.

The push-up plate 41 is located on an inner bottom surface of the sheet feed cassette 22 below the downstream portion of the lift plate 25, and located in the center of the lift plate 25 in the sheet width direction. As illustrated in FIG. 4, one end of the push-up plate 41 is fixed to a leading end of the rotation shaft 42 which is so arranged as to extend in the sheet width direction. The push-up plate 41 projects toward the radial outside of the rotation shaft 42.

The fan-shaped gear 43 is fixed to the rotation shaft 42. The fan-shaped gear 43 is located in a position close to a right side surface of the sheet feed cassette 22 and is located inside a gear holder 45 illustrated in FIGS. 4 and 5. The fan-shaped gear 43 is rotatable about an axial line extending in the sheet width direction orthogonal to the sheet conveying direction.

The lift side coupling gear 44 engages the fan-shaped gear 43. Similarly, the lift side coupling gear 44 is rotatable about an axial line extending in the sheet width direction. The lift side coupling gear 44 is located within the gear holder 45, as is the fan-shaped gear 43, and a part of the lift side coupling gear 44 is exposed to the outside from an opening portion 46 of the gear holder 45. The support unit of the lift side coupling gear 44 is described hereinafter.

Different from the lift plate lifter mechanism 40 with the above-mentioned design, the drive device 50 (see FIG. 6) is located outside the sheet feed cassette 22, at a position close to the right side surface of the main body 21 in the sheet supplying device 20 illustrated in FIG. 2. The drive device 50 includes a motor and a plurality of gears.

As illustrated in FIG. 6, the drive device 50 is provided with a drive side coupling gear 51 at an end of the plurality of gears. The drive side coupling gear 51 faces the right side surface of the sheet feed cassette 22, and is located at a position close to the sheet feed cassette 22. A part of the drive side coupling gear 51, below the downstream side in the sheet conveying direction, is exposed from an opening portion 52 of the drive device 50 toward the sheet feed cassette 22.

The drive side coupling gear 51 is located at a position corresponding to the lift side coupling gear 44 of the sheet feed cassette 22. With the above-mentioned design, as illustrated in FIG. 7, when the sheet feed cassette 22 is stored in the main body 21, the lift side coupling gear 44 and the drive side coupling gear 51 are engaged with each other. Accordingly, the drive device 50 transmits power to the lift plate lifter mechanism 40 through the lift side coupling gear 44 and the drive side coupling gear 51, thereby enabling the downstream end side of the lift plate 25 to move up to the sheet supply position.

The structure of the support unit of the lift side coupling gear 44 in the lift plate lifter mechanism 40 will now be described with reference to FIGS. 8 to 11, in addition to FIGS. 5 and 6. FIG. 8 is a perspective view illustrating the periphery of the lift plate lifter mechanism of the sheet feed cassette, which is the same as that in FIG. 5, with the gear holder and the gear group removed. FIG. 9 is a partially enlarged view illustrating portions of the lift side coupling gear and the drive side coupling gear viewed from the inside. FIG. 10 is a partially enlarged view illustrating portions of the lift side coupling gear and the drive side coupling gear, which are the same as those in FIG. 9, viewed from the inside with both of the gears separated from each other. FIG. 11 is a partially enlarged view illustrating portions of the lift side coupling gear and the drive side coupling gear, which are the same as those in FIG. 9, viewed from the inside wherein both of the gears are rotating.

The lift side coupling gear 44 has a shaft portion 44 a, both ends of which are rotatably supported by a bearing 47, located in a frame 22 a of the sheet feed cassette 22 illustrated in FIG. 8. A bearing 48 is located in the gear holder 45 as illustrated in FIG. 5.

As illustrated in FIG. 9, each of the bearings 47 and 48 is positioned in an elongated hole (a hole that is not a perfect circle) extending longitudinally in the sheet conveying direction, that is, in the substantially horizontal direction of the sheet supplying device 20. The direction along which the elongated holes, that constitute the bearings 47 and 48, is inclined with respect to a normal line N at a contact portion of the lift side coupling gear 44 with the drive side coupling gear 51. It also extends forward so as to separate from the normal line N. With the above-mentioned structure, the lift side coupling gear 44 can be displaced along the withdrawal and storage direction of the sheet feed cassette 22 and a direction of toward and away from, with respect to the drive side coupling gear 51.

The length of elongated holes of the bearings 47 and 48 is in a range of the length where the engagement of the lift side coupling gear 44 with the drive side coupling gear 51 is not released when the sheet feed cassette 22 is stored in the main body 21, even when the lift side coupling gear 44 is displaced (see FIGS. 9 and 11).

The drive side coupling gear 51 includes a shaft portion 51 a, both ends of which are rotatably supported by a bearing 53 of the drive device 50 as illustrated in FIG. 6 (a bearing far from the sheet feed cassette 22 side is not shown). As illustrated in FIG. 9, the bearing 53 has a circular configuration. Accordingly, the drive side coupling gear 51 is not displaced along the withdrawal and storage direction of the sheet feed cassette 22.

In the above-mentioned method, the sheet supplying device 20 includes the sheet feed cassette 22 on which sheets P are loaded, and which can be pulled out and accommodated in a direction parallel to the sheet conveying direction with respect to the main body 21. It also includes the lift plate 25 which is located within the sheet feed cassette 22, and on a top surface of which the sheets P are placed, the lift plate lifter mechanism 40 which is located in the sheet feed cassette 22, and pushes up the lift plate 22 to displace the lift plate 25 to a sheet supply position, and the drive device 50 which is located in the main body 21, and transmits power to the lift plate lifter mechanism 40. The drive device 50 of the lift plate lifter mechanism 40 includes the drive side coupling gear 51 that is coupled with the lift plate lifter mechanism 40 when the sheet feed cassette 22 is stored in the main body 21. The lift plate lifter mechanism 40 is located on a side surface of the sheet feed cassette 22. The lift plate lifter mechanism 40 includes the lift side coupling gear 44 which is engaged with the drive side coupling gear 51 of the drive device 50 when the sheet feed cassette 22 is stored in the main body 21. The lift side coupling gear 44 is displaceably supported in a direction toward and away from with respect to the drive side coupling gear 51 in a range where engagement is not released. Accordingly, a slight gap can be defined between the drive side coupling gear 51 and the lift side coupling gear 44. As a result, an allowance with respect to rotation is provided between both gears, thereby making it possible to prevent a high load from being applied when the sheet feed cassette 22 is withdrawn from the main body 21. Additionally, the teeth of the gears do not collide with each other when the sheet feed cassette 22 is stored in the main body. The support mechanism of the lift side coupling gear 44 can be achieved with a simple design. Accordingly, with a simple design that reduces the costs, there can be provided the device for supplying sheets 20 which is capable of smoothly conducting the withdrawal and storage of the sheet feed cassette 22, readily storing the sheet feed cassette 22 at an appropriate position, and performing a stable sheet feeding operation.

The sheet feed cassette 22 includes the support portion of the lift side coupling gear 44, which is provided with the elongated hole and is capable of displacing the lift side coupling gear 44 in a direction of toward and away from with respect to the drive side coupling gear 51. As a result, with a simpler design, the support mechanism of the lift side coupling gear 44 can be achieved. Accordingly, with a design that further reduces the costs, the withdrawal and storage of the sheet feed cassette 22 can be smoothly performed, and the sheet feed cassette 22 can be stored at an appropriate position with ease.

The lift side coupling gear 44 moves within the elongated hole in a direction away from the drive side coupling gear 51 while rotating in the direction indicated by the broken line arrow in the figure. The lift side coupling gear 44 and the drive side coupling gear 51 come into contact with each other at the time of storage of the sheet feed cassette 22 in the main body 21, from a relationship of the abutment portion (circle A in the figure) of the lift side coupling gear 44 with the drive side coupling gear 51 and the direction along which the elongated holes of the bearings 47 and 48 extend as illustrated in FIG. 10.

The elongated holes of the bearings 47 and 48 are designed so that the lift side coupling gear 44 moves in a direction away from the drive side coupling gear 51 while rotating when the drive side coupling gear 51 comes into contact with the lift side coupling gear 44 at the position indicated by circle A in FIG. 10. This design makes it possible to enhance the effect of preventing the teeth of the lift side coupling gear 44 and the drive side coupling gear 51 from colliding with each other when the sheet feed cassette 22 is stored in the main body 21. With this design, the lift side coupling gear 44 and the drive side coupling gear 51 are easily engaged with each other. Accordingly, the storage of the sheet feed cassette 22 can be more further smoothly performed, whereby it is possible to improve the advantageous effect of storing the sheet feed cassette 22 at an appropriate position, and performing the stable sheet feed operation.

When the power is transmitted to the lift plate lifter mechanism 40 by the drive device 50, so as to move up the lift plate 25 to the sheet supply position, the drive side coupling gear 51 rotates clockwise, and the lift side coupling gear 44 rotates counterclockwise, as viewed from inside of the sheet feed cassette 22 as illustrated in FIG. 11. As a result, the lift side coupling gear 44 is about to move while rotating from the front side toward the rear side of the elongated holes of the bearings 47 and 48, from the right side toward the left side in FIG. 11.

When the lift side coupling gear 44 rotates, the lift side coupling gear 44 is displaced in a direction toward the drive side coupling gear 51 due to rotation force. As a result, even though a gap is provided between the lift side coupling gear 44 and the drive side coupling gear 51, which are engaged with each other, both of the gears easily engage each other. Accordingly, there can be provided a device for supplying sheets 20 which is capable of performing a stable sheet feeding operation.

In an embodiment of the present invention, since the device for supplying sheets 20 is mounted on the printer 1, with the simple design that reduces costs, there can be provided a printer 1 which is capable of smoothly conducting the withdrawal and storage of the sheet feed cassette 22, easily storing the sheet feed cassette 22 at an appropriate position, and performing the stable sheet feeding operation.

It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims. 

1. A device for supplying sheets, comprising: a sheet feed cassette in which sheets are stacked, and which can be pulled out and stored in a direction parallel to a sheet conveying direction with respect to a main body of an apparatus; a lift plate which is located within the sheet feed cassette, and which has a top surface on which the sheets are placed; a lift plate lifter mechanism which is located in the sheet feed cassette, for moving up the lift plate to displace the lift plate to a sheet supply position; a drive device which is located in the main body of the apparatus, for providing power to the lift plate lifter mechanism; the drive device comprises a drive side coupling gear that is coupled with the lift plate lifter mechanism when the sheet feed cassette is stored in the apparatus main body; and the lift plate lifter mechanism comprises a lift side coupling gear which is located at a side surface of the sheet feed cassette, engaged with the drive side coupling gear of the drive device when the sheet feed cassette is stored in the main body, and is moveably supported in a direction toward and away from with respect to the drive side coupling gear in a range wherein the engagement of the gears is not released.
 2. A device for supplying sheets according to claim 1, wherein the sheet feed cassette has an elongated hole on a support portion of the lift side coupling gear, the elongated hole being capable of displacing the lift side coupling gear in a direction toward and away from with respect to the drive side coupling gear.
 3. A device for supplying sheets according to claim 2, wherein the elongated hole extends in the direction that the lift side coupling gear separates from the drive side coupling gear while rotating when the lift side coupling gear and the drive side coupling gear come in contact with each other.
 4. A device for supplying sheets according to claim 1, wherein, when the lift side coupling gear rotates, the lift side coupling gear is displaced in a direction toward the drive side coupling gear due to rotation force.
 5. An image forming apparatus, comprising: a device for supplying sheets comprising a sheet feed cassette in which sheets are stacked and which can be pulled out and stored in a direction parallel to a sheet conveying direction with respect to a main body of an apparatus; a lift plate which is located within the sheet feed cassette, and which has a top surface on which the sheets are placed; a lift plate lifter mechanism which is located in the sheet feed cassette, for moving up the lift plate to displace the lift plate to a sheet supply position; a drive device which is located in the main body, the drive device comprises a drive side coupling gear that is coupled with the lift plate lifter mechanism when the sheet feed cassette is stored in the main body; and the lift plate lifter mechanism comprises a lift side coupling gear which is located at a side surface of the sheet feed cassette, engaged with the drive side coupling gear of the drive device when the sheet feed cassette is stored in the main body, and is displaceably supported in a direction of toward and away from with respect to the drive side coupling gear in a range where the engagement of the gears is not released.
 6. A device for supplying sheets, comprising: a sheet feed cassette in which sheets are stacked, and which can be pulled out and stored in a main body of an apparatus; a lift plate which is located within the sheet feed cassette; a lift plate lifter mechanism which is located in the sheet feed cassette, for moving up the lift plate to a sheet supply position; a drive device which is located in the main body of the apparatus, for providing power to the lift plate lifter mechanism; the drive device comprises a drive side coupling gear that is coupled with the lift plate lifter mechanism when the sheet feed cassette is stored in the apparatus main body; and the lift plate lifter mechanism comprises a lift side coupling gear engaged with the drive side coupling gear of the drive device when the sheet feed cassette is stored in the main body, and is moveable toward and away from the drive side coupling gear without the engagement of the gears being released. 